Magnetic resonance power technology is the near-field wireless transmission of electrical energy between a transmitter coil and a receiver coil that are tuned to resonate at the same frequency. Based on the principles of electromagnetic coupling, resonance-based chargers inject an oscillating current into a highly resonant coil to create an oscillating electromagnetic field. A receive coil with the same resonant frequency located close by receives power from the electromagnetic field and converts it back into electrical current that can be used to power and charge a portable device. Resonance charging offers unique advantages in spatial freedom, enabling the transmitter (resonance charger) to be separated from the receiver (portable device) by up to several inches or more.
Knowledge of the peak-to-peak voltage across the resonant transmitter's primary inductor L or primary capacitor C during power transfer is needed for high frequency resonant power management systems. A conventional method to measure the peak-to-peak voltage during operation of the resonant transmitter is to use a fast differential amplifier with high common mode rejection to process the signal which is generally at a high frequency, such as being driven by a class-D driver switched at the US Federal Communication Commission (FCC) allowed frequency of 6.78 MHz. The peak-to-peak voltage across the capacitor C is generally easiest to measure compared to the peak-to-peak voltage across the primary L which can also technically be used for this purpose, but is complicated by step jumps resulting from the driver's pulsed drive signals.